Defoliation triggered by climate induced effects in Spanish ICP Forests monitoring plots

In a context of global change, climate impacts can trigger defoliation processes in different forest species. The ICP Forests network estimates the level of forest defoliation over time in different European countries. Those data are used to related defoliation with potential causal factors. In European Southwestern forests, climate change appears to be the detonating factor of generalized defoliation. The objectives of this study were: (i) identity defoliation trends in forest trees at network of Spanish ICP Forests monitoring plots and, (ii) find out if there are underlying climate factors that trigger defoliation process along the time. The spatiotemporal synchronization of the defoliation response was analyzed with cross-correlation using COFECHA software. The relationship between the 88 climatic variables proposed and defoliation was analyzed using Correlated Component Regression models (CCR models) and Discriminant Analysis (DA). The significance of the variables in each model was compared using contingency tables. A peak of defoliation was observed in the mid-1990s with no recovered to the initial values of the early 1990s. The behavior of the different tree species with respect to defoliation, synchronized both in time and space, involves one or several factors that have a general and similar effect on forests in Spain. The most significant factors related to defoliation were the thermal-related factors, particularly average temperatures in April and June and the thermal oscillation of both the current year and the previous year. Only one drought indicator as statistically significant was identified (A, duration of aridity in months) and suggests that it is of limited relevance in the Spanish forest defoliation conditions.